Tires are sometimes prepared with treads of rubber compositions comprised of diene-based elastomers which contain reinforcement as carbon black and/or silica in combination with a coupling agent to aid in coupling the silica and/or hydroxyl terminated liquid ethylene/butylene copolymer to diene-based elastomers.
While rubber processing oils have often been used to improve processability (e.g. to reduce rubber viscosity) of various unvulcanized relatively high viscosity elastomers, as well as to substantially maintain various physical properties for various conjugated diene-based elastomers for various tire components, the inclusion of relatively medium to large rubber processing oil contents in such diene-based rubber compositions often results in an unwanted decrease of various significant rubber physical properties so that such use of significant quantities of rubber processing oils in the respective rubber compositions for various tire components may not be a desirable option.
In one respect, it has heretofore been proposed to use various diene-based liquid polymers which contain olefinic unsaturation to replace at least a portion of rubber processing oil which might otherwise be contained in the respective rubber composition for a tire component. One philosophy has been for the liquid diene-based polymer to initially enhance the processsability of a relatively high viscosity unvulcanized rubber composition (e.g. reduce its viscosity) and to later co-sulfur vulcanize with the diene-based elastomer via the olefinic double bonds contained in the liquid diene-based polymer upon sulfur vulcanizing the rubber composition.
In another aspect, replacement of conventional rubber processing oils with a hydroxyl terminated liquid polyalkylene-based polymer in a sulfur cured tire sidewall rubber composition composed of cis 1,4-polybutadiene, brominated copolymer of isobutylene and para-methylstyrene and a minor amount of cis 1,4-polyisoprene has been suggested in U.S. Pat. No. 6,255,397 as well as U.S. Pat. No. 6,251,992 in which the brominated copolymer of isobutylene and para-methylstyrene is not included.
For this invention, an hydroxyl terminated liquid saturated ethylene/butylene backbone polymer having an hydrogenated polyisoprene block or epoxidized polyisoprene block on the opposite end of the ethylene/butylene copolymer backbone (in addition to its aforesaid hydroxyl terminal group) is used which becomes a part of a sulfur cured network, in combination with the included conjugated diene-based elastomer(s) of the rubber composition for a tire component.
However, it remains desirable to continue to improve various properties and/or processability of various conjugated diene-based rubber compositions for various tire components.
In the description of this invention, the term “phr” as used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber elastomer”. In the description of this invention, the terms “rubber” and “elastomer” can be used interchangeably, unless otherwise distinguished. The terms “rubber composition”, “compounded rubber” and “rubber compound” can be used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and the terms “cure” and “vulcanize” may also be used interchangeably herein, unless otherwise noted and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
The term “butyl-type” polymers or rubbers relates to isobutylene copolymers comprised of isobutylene and a minor amount of conjugated diene (e.g. from about 0.5 to about 3 weight percent conjugated diene such as for example isoprene), which are conventionally referred to as butyl rubbers, as well as halogenated (e.g. brominated or chlorinated) butyl rubber as well as copolymers, particularly brominated copolymers, of isobutylene and para methylstyrene.